Electronic absorption and E.S.R. spectra of the benzene and paracyclophane anions

Abstract

The electronic absorption and E.S.R. spectra of the benzene and 2,2-paracyclophane anions were measured. The paracyclophane anion showed a strong absorption band at 760 mμ and an E.S.R. pattern with hyperfine structures of 41 lines. On the other hand, the benzene anion had an absorption peak at 420 mμ and an S.E.R. spectrum with hyperfine structures of seven lines. Combining these experimental results with a molecular orbital calculation taking account of configuration interaction, we were led to the conclusion that there exists an electron resonance interaction between the π electron systems belonging to the two benzene rings of the paracyclophane anion and that the exchange interaction energy between them amounts to 0·82 ev. Furthermore, the 760 mμ band was interpreted to be a charge-(or electron) resonance absorption caused by the electron-resonance interaction. The π-electron structure of the biphenyl anion was also studied theoretically and the result was compared with that for the paracyclophane anion.